1. Field of the Invention
The present invention relates to an operating system for an internal combustion engine which operates the internal combustion engine by using a high-octane fuel and a low-octane fuel.
2. Related Background Art
Conventionally, as disclosed in, for example, Japanese Patent Laid-open No. 2009-293600 (hereinafter, referred to as Patent Document 1) and Japanese Patent Laid-open No 2000-329013 (hereinafter, referred to as Patent Document 2), there has been known an operating system which is configured to separate a mixed fuel (raw fuel) containing plural fuel components of different octane numbers into a first fuel having a higher concentration of high-octane fuel number components than the raw fuel (first fuel having a higher octane number than the raw fuel) and a second fuel having a lower concentration of high-octane fuel number components than the raw fuel (second fuel having a lower octane number than the raw fuel) by using a separation device, and operate an internal combustion engine by using the first fuel and the second fuel obtained from the separation device.
In such kind of operating system, it is expected to prevent knockings from occurring and to improve the millage by controlling variably according to the operation of the internal combustion engine the ratio of a supplied amount of the high-octane number fuel components (hereinafter, referred to as high-octane fuel) in the fuels supplied to a combustion chamber of the internal combustion engine.
In the internal combustion engine operated by the above-mentioned operating system, the occurrence of knockings can be prevented by increasing the supply ratio of the high-octane fuel to the combustion chamber in a high-load operation; therefore, it is possible to improve output performance (to increase the upper limit of an available output torque) of the internal combustion engine.
However, if the first fuel having a high concentration of the high-octane fuel is frequently consumed, the first fuel will become less and less, and the second fuel having a lower concentration of the high-octane fuel will be excessively remained. In such a situation, since the first fuel is impossible to be consumed any further, more of the second fuel having a low concentration of the high-octane fuel will have to be consumed. Accordingly, it is difficult to prevent the occurrence of knockings in the high-load operation, and consequently, the output performance of the internal combustion engine should be limited.
Therefore, it is desirable the consumed amount of the high-octane fuel by the internal combustion engine which needs the high-octane fuel to be supplied to the combustion chamber thereof in operation should be as less as possible.
On the other hand, in order to improve the output performance of the internal combustion engine while preventing the knockings from occurring, generally, it is advantageous that the octane number to be combusted in the combustion chamber of the internal combustion engine is higher. Thus, as seen in the conventional systems disclosed in Patent Documents 1 and 2, it is common that the separation of the raw fuel is performed to decrease the concentration of the low-octane fuel components contained in the first fuel is as low as possible, in other words, to increase the concentration of the high-octane fuel components contained in the first fuel as high as possible (and consequently, to increase the octane number of the first fuel).
However, as to be described hereinafter, after studied various experiments, the inventors of the present application have discovered that if the concentration of the high-octane fuel contained in the first fuel is high, an excessive amount of the high-octane fuel which is more than the necessary amount appropriate for preventing the occurrence of the knockings would be supplied to the combustion chamber of the internal combustion engine in a normal operation state of the internal combustion engine.